Bombardment cutter



March 22, 1966 H. WING 3,241,265

BOMBARDMENT CUTTER Filed June 27, 1963 2 Sheets-Sheet 1 March 22, 1966 H. WING 3,241,265

BOMBARDMENT CUTTER Filed June 2'7, 1965 2 Sheets-Sheet 2 FIG. 3 68 52 United States Patent 3,241,265 BOMBARDMENT CUTTER Henry Wing, Wappingers Falls, N.Y., assignor to International Business Machines Corporation, New York, N .Y., a corporation of New York Filed June 27, 1963, Ser. No. 291,133 Claims. (Cl. 519) This invention relates to a means for cutting and more particularly to a means for cutting which employs high frequency abrasive bombardment.

In the production of semiconductor devices, many methods have been employed to cut germanium and silicon wafers into suitable sized dice. One of the first cutting methods in the art employed the use of the diamond saw, but due to the difiiculty of obtaining saws of thin accurate dimensions, alternative methods of cutting came into favor. The most widely used alternative cutters now employ ultrasonic phenomena. These cutters generally provide a lattice-work cutter which is positioned over a semiconductor wafer and affixed to an ultrasonic transducer. To provide the cut, an abrasive slurry is introduced between the cutter head and the semiconductor wafer while the transducer is caused to vertically oscillate at a frequency above the audible range, e.g., 20-30,000 c.p.s. By causing the cutter to oscillate at such a high frequency, extremely high accelerations are imparted to the particles in the slurry which cause them to bombard the wafer and produce the desired cut. Such a cutter is described in US. Patent 2,774,194.

There are two major problems with the above-described cutters. First, the manufacturing cost of the lattice-work cutting element is high, it having to be machined to extremely high tolerances and moreover to be discarded should any error occur during any portion of its production. Secondly, the ultrasonic transducer and power supply are high cost items and require special mounting facilities due to the structural rigidity needed for accommodating of the high frequency rectilinear motion.

Accordingly, it is an object of this invention to provide an improved ultrasonic cutter.

It is another object of this invention to provide an ultrasonic cutter which utilizes an inexpensive and simple cutting element.

It is still another object of this invention to provide an ultrasonic cutter which has no requirement for linear oscillations of the cutter.

It is still another object of this invention to provide an ultrasonic cutter wherein a number of simultaneous cuts can be made.

Still another object of this invention is to provide an ultrasonic cutter which utilizes a cutting element of extremely long life.

In accordance with the above objects, a disc rotating at high speed has a jet of abrasive slurry directed at its edge. A supersonic acceleration is thereby imparted to the deflected abrasive slurry particles. By then placing a wafer to be cut in a noncontacting but proximate positionto the point of contact between the slurry and the disc, the deflected and accelerated slurry particles are caused to erode the wafer in the desired manner.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a schematic embodiment of the invention.

FIG. 2 is an enlarged side view of FIG. 1 for schematically showing the cutting action.

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FIG. 3 is a front view of a practical embodiment of the invention.

FIG. 4 is a plan view of the mechanism shown in FIG. 3.

FIG. 5 is a showing of the semiconductor wafer after it has been cut.

Referring now to FIG. 1, a semiconductor material 10 such as silicon or germanium. has previously been deposited upon epoxy plastic or glass substrate 12. Disposed over semiconductor wafer 10 is a slurry nozzle 14 out of which there continually emanates a flow of a liquid abrasive or slurry.

A suitable slurry has been found to be a suspension of silicon carbide particles in water. Mounted on axis 16 is cutting disc 18 which is rigidly held in place by retainer discs 20 and 22. Suitable materials for cutting disc 18 are stainless steel, or high cobalt stainless. This is not to say that softer metals cannot be utilized; however, it has been found that for this particular application, the aforementioned stainless steels provide the longest life for the blade.

Motive means (not shown) are provided to impart a high rotational speed to shaft 16 and in turnto cutting disc 18. Satisfactory results have been obtained by causing the edge 24 of disc 18 to rotate at a speed of 10,000 linear feet per minute. The aforementioned circumferential speed of disc 18 should not be thought. of as limiting the invention as hereinafter described since linear speeds both higher and lower than the recited 10,000 feet per minute also allow the cutting device to function as contemplated.

Disc 18 is vertically movable by virtue of the fact that shaft 16 is rotatably mounted on arm 26. Arm 26 is pivoted at pin 28 to a fixed member 30. Mounted at the opposite end of arm 26 is counterbalance 32 which performs the function of adjusting the weight which disc 18 bears upon wafer 10. Normally, counterbalance 32 is adjusted such that the downward force exerted by disc 18 is just sufficient to overcome the upward force created when the slurry flow from nozzle 14 impacts upon edge 24.

In operation, disc 18 is brought up to full speed and then the slurry flow from nozzle 14 is initiated. When disc 18 is rotating at the desired speed, a thin air barrier or windage is created which envelopes edge 24. It is created by the friction between edge 24 and the surrounding air which tends to cause the air to follow the edge as it rotates. The windage therefore sets up an air barrier between edge 24 and the existing slurry from nozzle 14. It is therefore necessary to impart a suficient velocity to the slurry to overcome the aforementioned air barrier and to allow it to impact upon the edge 24 of disc 18.

FIG. 2 shows an enlarged view of the cutting area of FIG. 1 and will be referred to hereinafter in conjunction with FIG. 1 as the explanation of the operation of the invention progresses. The arrows enumerated 34 are representative of the liquid slurry flow. When disc 18 is rotating at its specified cutting speed, and the slurry flow from nozzle 14 has a sufiiciently high velocity to overcome the windage surrounding edge 24 so that the liquid slurry 34 actually impacts upon the edge 24, wafer 10 is moved towards disc 18. As the leading edge of wafer 10 arrives in the proximity oflbut does not touchedge 24, the cutting action begins.

The cutting phenomenon is the result of two major factors, the first being the downward acceleration which is imparted to the actual abrasive particles in. the slurry as they impact upon edge 24 of disc 18, and the second being the acceleration imparted to the liquid abrasive itself by edge 24. The result is a bombardment action which causes erosion of only the material directly beneath edge =3 24. It must here be emphasized that it is not a contact phenomenon between disc 18 and wafer 10 which provides the cutting action, but rather it is an erosive action which results from the bombardment of the accelerated abrasive particles and slurry. Experimentally, it has been found that so long as there is no actual contact between disc 18 and wafer 10, that an extremely clean cut of accurate dimensions is produced. There is also little or no vertical movement of disc 18 (remembering that its downward load is just suflicient to overcome the upward force produced by slurry 34). However, when accidental contact occurs between disc 18 and wafer 10, the cut becomes irregular and ragged, with portions of the wafer being chipped; and disc 18 begins oscillating up and down as would a bouncing ball. To prevent this phenomenon from occurring, the mechanism (not shown) which feeds wafer 10 towards disc 18 must have its speed set such that the speed of feed is less than the rate of erosion of wafer 10. Since the rate of feed is directly related to the speed of rotation from disc 18, the rate of flow and type of abrasive slurry and the hardness of wafer 10, to determine the rate of feed theoretically is rather complex. But (as will hereinafter be described), it is a rather simple matter to determine empirically.

Referring now to FIGS. 3 and 4, there is shown both top and side views of a practical embodiment of the invention. Referring first to FIG. 4, shaft 40 has rigidly mounted thereon cutting element 42. Cutting element 42 is comprised of a plurality of stainless steel cutting discs 44 with interspersed spacers 46. For the particular application under consideration, i.e., that is the cutting of semiconductor substrates, disc 44 may have a thickness of approximately 2 mils and an outside diameter of 4 inches. Spacers 46 allow only approximately 20-40 mils of the cutting discs to be exopsed to the device being cut. This provides for the necessary rigidity of the discs while turning at the above-mentioned high speeds. The number of discs 44 and spacers 46 may be multiplied in accordance with the desired number of cuts to be produced.

Shaft 40 is rotatably mounted in casting 56 and is caused to rotate by belt 48 which couples pulley 50 with motor driven pulley 52. Casting 56, is pivotally mounted in fixed member 60 by shaft 58. Fixed member 60 is in turn fixedly attached to platform 80 (FIG. 3). Motor 54, which provides the motive power for pulley 52 is mounted on pivot plate 66. Pivot plate 66 is in turn pivotally journalled into arm portions 62 and 64 of casting 56. To provide means for adjusting the tension of belt 48, adjustment device 68 (FIG. 3) is provided. Fixedly attached to and rotatable with casting 56, is arm 70.

The mechanical positioning of shaft 58 with respect to cutter 42, shaft 40, motor 54, casting 56 and arm 70, etc., is such that the aforementioned elements are nearly balanced. Due to the fact, however, that pivot plate 66 and motor 54 are movable for the purposes of adjusting the tension of belt 48, this balance cannot always be insured. For this reason (FIG. 3) adjustable spring tension element 72 is provided which, in accordance with its adjustment, provides a counteracting force for any unbalance in the device. In fact, since a small downward pressure is desired n cutters 42 to counteract the upward force imparted by the slurry flow (as aforementioned), spring tension device 72 is normally adjusted to provide such. A suitable adjustment has been found to be approximately ounces per cutting disc.

One end of arm 70 has a flattened out portion 74 on which plunger 76 rides. Attached to the other end of plunger 76 is displacement gauge 77 which is fixedly mounted by arm 78 to platform 80. The main purpose for displacement gauge 77 is to indicate when cutters 44 are actually engaging and touching the wafer being cut. The bouncing resulting from this contact is sufficient to cause the gauge indicator to gyrate. This indication is helpful in setting the feed rate of the Wafer.

Wafer 81 and its associated substrate 82 (FIG. 3) are mounted on table 84 which is in turn affixed to shafts 86 and 88. Shafts 86 and 88 are slidably mounted in platform and are driven by motive means (not shown) to provide the lateral movement which is necessary to pass wafer 81 beneath cutter 42. Bellows 90 and 92 (a portion of which is shown in FIG. 4) prevent the slurry which is constantly being passed over wafer 81 from getting into the sliding joints between shafts 86 and 88 and platform 80.

Also attached to platform 80 is slurry nozzle 94 which provides the required slurry flow. The slurry is introduced into the nozzle through tube 96 from a slurry pump (not shown). With the speed of rotation of cutting element 42 at approximately 10,000 linear feet per minute, it has been found that a slurry velocity of 30 feet per second emanating from nozzle 94 is sufliciently effective to overcome the windage which is created by virtue of the high speed rotation. It should be emphasized that the slurry itself (without the acceleration imparted to it by cutter 42) has not sufiicient velocity to perform any cutting or bombarding action. The nozzle opening of slurry nozzle 94 can be made as wide or as narrow as desired depending upon the size of the wafer to be cut. To determine the rate of feed of wafer 81 into the vicinity of cutter 42, only a single run is needed. During this set-up run, the speed of feed is set as low as possible, e.g., less than 1 inch per minute. As the cutting action begins, the rate of feed is gradually increased, keeping constant watch on dial indicator 77 until it begins to gyrate. At this point, the rate of feed is just beginning to exceed the rate of erosion of wafer material 81. By then backing off somewhat from the aforementioned speed, the optimum rate of feed is determined and may be maintained throughout repetitive operations. For the particular speeds and rate of slurry flow above mentioned, it has been found that a feed rate of 3 inches per minute is satisfactory.

In FIG. 5, there is shown a view of the semi-conductor wafer after it has been cut. It has been found that with a 2 mil cutting disc, that the kerf between adjacent dice approximates 4 mils. To produce the diced effect, the wafer is first cut in one direction and then rotated 90 degrees and out again. Each dice has approximate dimensions of 25 x 25 mils.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. For instance, while representative cutter rotation feed and slurry speeds have been given, it is obvious that other combinations will work equally well.

I claim: 1. In a device for cutting a workpiece, the combination which comprises:

a disc; means for rotating said disc at a high peripheral speed; nozzle means for directing an abrasive slurry at said disc, said nozzle means imparting a sufficiently high fluid velocity to said slurry to cause said slurry to impact upon said disc and be accelerated thereby;

means for balancing said disc to cause said disc to exert sufficient force to overcome any opposing force created by the impact of said abrasive slurry on said disc; and

motive means for bringing said disc and said workpiece in sufficiently close proximity to allow said accelerated slurry to bombard and erode said workpiece.

2. In a device for cutting a workpiece, the combination which comprises:

a disc;

means for rotating said disc at a high peripheral speed;

means for directing an abrasive slurry at said disc,

said means imparting a suflicient fluid, velocity to said slurry to cause said slurry to impact upon said disc and be accelerated thereby;

means for balancing said disc to cause said disc to exert suflicient force to overcome any opposing force created by the impact of abrasive slurry on said disc; support means for holding a workpiece; and

motive means for bringing said support means and said disc into sufliciently close proximity to allow said accelerated slurry to bombard and erode any workpiece held by said support means. i 3. In a device for cutting a workpiece, the combination which comprises:

a disc; means for rotating said disc at a high peripheral speed; nozzle means for directing an abrasive slurry at said disc, said nozzle means imparting a suflicient fluid velocity to said slurry to cause said slurry to impact upon said disc and be accelerated thereby;

means for balancing said disc to cause said disc to exert suflicient force to overcome any opposing force created by the impact of said abrasive slurry on said disc; support means for holding a workpiece; and motive means for moving said support means and said disc into sufficiently close proximity to allow said accelerated slurry to bombard and erode a portion of a held workpiece, the rate of removal of said portion of said workpiece being greater than the rate of relative movement between said support means and said disc. 4. The invention as defined in claim 3 with the addition of gauge means operatively coupled to said disc for indicating eccentric motion of said disc when and if contact is established between said disc and said device.

5. In a device for cutting a workpiece, the combination which comprises:

a disc; means for rotating said disc at a high peripheral speed; nozzle means for directing an abrasive slurry at said disc, said nozzle means imparting a suflicient fluid velocity to said slurry to cause said slurry to impact upon said disc and be accelerated thereby;

means for balancing said disc to cause any downward force exerted by said disc to just overcome any upward force caused by said abrasive slurry impacting on said disc,

means for supporting a workpiece; and

motive means for bringing said support means and said disc into sufficiently close proximity to allow said accelerated slurry to bombard rand erode any workpiece held by said support means. 6. In a device for cutting a workpiece, the combination which comprises:

a disc; means for rotating said disc at a high peripheral speed; nozzle means for directing an abrasive slurry at said disc, said nozzle means imparting a sufficient fluid velocity to said slurry to cause said slurry to impact upon said disc and be accelerated thereby;

means for balancing said disc to cause any downward force exerted by said disc to just overcome any upward force caused by said abrasive slurry impacting on said disc;

means for supporting a workpiece;

motive means for moving said support means and said disc into sufficiently close proximity to allow said eccelerated slurry to bombard and erode a portion of a held workpiece, the rate of removal of said portion of said workpiece being greater than the rate of relative movement between said support means and said disc; and

gauge means operatively coupled to said disc for indicating eccentric motion of said disc when and if contact is established between said disc and said device.

7. In a device for cutting a workpiece, the combination which comprises:

a disc having a peripheral edge;

means for rotating said disc at a high peripheral speed;

nozzle means for directing an abrasive at said peripheral edge, said nozzle means imparting a sufliciently high velocity to said abrasive to cause said abrasive to impact upon said edge and be deflected and accelerated thereby; and

motive means for providing relative tangential movement between said disc edge and said workpiece to bring said edge and workpiece into sufliciently close proximity to allow said deflected, accelerated abrasive to bombard and erode said workpiece.

8. In a device for cutting a workpiece, the combination which comprises:

a disc having a peripheral edge;

means for rotating said disc at a high peripheral speed;

means for directing an abrasive slurry at said edge, said means imparting a suflicient fluid velocity to said slurry to cause said slurry to impact upon said disc edge and be deflected and accelerated thereby;

support means for holding a workpiece; and

motive means for providing relative tangential movement between said support means and said disc edge to bring said support means and said disc edge into sufliciently close proximity to allow said deflected accelerated slurry to bombard and erode any workpiece held by said support means.

9. In a device for cutting a workpiece, the combination which comprises:

a disc having a peripheral edge whose width defines the thickness of a desired cut;

means for rotating said disc at a high peripheral speed;

nozzle means for directing an abrasive slurry at said edge, said nozzle means imparting a sufiicient fluid velocity to said slurry to cause said slurry to impact upon said disc edge and be deflected and accelerated thereby;

support means for holding a workpiece; and

motive means for providing relative tangential movement between said support means and said disc edge to bring said support means and said disc edge into sufliciently close proximity to allow said deflected accelerated slurry to bombard and erode a portion of a held workpiece, the rate of removal of said portion of said workpiece being slightly faster than the rate of relative movement between said support means and said disc.

10. In a device for making a plurality of parallel cuts in a workpiece, the combination which comprises.

a plurality of discs each said disc separated from each other by a spacer and provided with a peripheral edge whose width defines the thickness of a desired cut;

means for rotating said discs at a high peripheral speed;

nozzle means for directing an abrasize slurry at the peripheral edges of said discs, said nozzle means imparting a sufficient fluid velocity to said slurry to cause said slurry to impact upon said disc edges and be deflected and accelerated thereby;

means for supporting a workpiece; and

motive means for providing relative tangential movement between said support means and said disc edges to bring said support means and said disc edges into suificiently close proximity to allow said deflected accelerated slurry to bombard and erode portions of a held workpiece, the rate of removal of said portions of said workpiece being greater than the rate of relative movement between said support means and said disc edges.

(References on following page) 7 8 References Cited by the Examiner 2,135,550 11/ 1938 Alexander 51--9 2,663,980 12/1953 Harper 519 X UNITED STATES PATENTS 3,081,586 3/1963 Gersbach 51 2s3 217,709 7/1879 Sawyer 519 2,092,962 9/1937 Fay et all 5 LESTER M. SWINGLE, Primary Examiner. 

7. IN A DEVICE FOR CUTTING A WORKPIECE, THE COMBINATION WHICH COMPRISES: A DISC HAVING A PERIPHERAL EDGE; MEANS FOR ROTATING SAID DISC AT A HIGH PERIPHERAL SPEED; NOZZLE MEANS FOR DIRECTING AN ABRASIVE AT SAID PERIPHERAL EDGE, SAID NOZZLE MEANS IMPARTING A SUFFICIENTLY HIGH VELOCITY TO SAID ABRASIVE TO CAUSE SAID ABRASIVE TO IMPACT UPON SAID EDGE AND BE DEFLECTED AND ACCELERATED THEREBY; AND MOTIVE MEANS FOR PROVIDING RELATIVE TANGENTIAL MOVE- 